Albert Barnes Commentary 2 Kings 10:13

"Jehu met with the brethren of Ahaziah king of Judah, and said, Who are ye? And they answered, We are the brethren of Ahaziah: and we go down to salute the children of the king and the children of the queen." — 2 Kings 10:13 (ASV)

The brethren of Ahaziah - Not the actual brothers of Ahaziah, who had all been slain by the Arabs before his accession to the throne (2 Chronicles 21:17; 2 Chronicles 22:1), but his nephews, the sons of his brothers. It is remarkable that they should have penetrated so far into the kingdom of Israel without having heard of the revolution.

The children of the king ... - That is, the sons of Jehoram, and the children (sons and grandsons) of the queen-mother, Jezebel. Some of both may well have been at Jezreel, though the younger branches of the royal family were at Samaria (2 Kings 10:1).